This may be a method name or a code reference that can be run in order to coerce the control's current value to the action attribute's value during action processing. The given method or subroutine will always be called with 3 arguments:

This is either a method name (to be called on the action the control is connected with) to a code reference. This method or subroutine will be called to conver the action attribute value to the control's value.